The invention relates to a propulsion control which uses wheel or axle rotational speed and vehicle longitudinal acceleration as control inputs to a vehicle propulsion control system.
Such a device is shown in U.S. Pat. No. 4,763,262. This device is a drive slip control arrangement with various slip thresholds which are switched over or selected in dependence, among other things, on the vehicle longitudinal acceleration.
It is very important, particularly in the case of propulsion controls, to recognize early when the driven wheels are spinning, for example during the starting from a vehicle standstill. Conventional rotation speed sensor signal can only be obtained above circumferential wheel speeds of approximately 2.5 km/h. In this range, however, there may already be such a large excess torque, that traction and lateral control are very low. It is therefore the aim of an optimum propulsion control system to keep the control deviation as small as possible even in the first control cycle. However, this is hindered by the resolving capacity of the speed-of-rotation sensors. Although high-resolution speed-of-rotation sensors are known, these are not used in series production because of the high cost.
It is therefore the object of the invention to create a propulsion control which enables high excessive torques to be recognized early at supportable costs.
According to the invention, this object is achieved as follows.
According to this, only the sensors of the driven wheels (in the case of four-channel control) or the sensor at the driving pinion of the driven axle (in the case of three-channel control) are high-resolution speed-of-rotation transmitters, while the sensors of the non-driven wheels are inexpensive speed-of-rotation sensors of the conventional type of construction. In a speed range, for example below 5 km/h, in which the sensors of the non-driven wheels do not yet supply a usable signal for the vehicle speed or acceleration, the signal of a difference is formed between the acceleration of the driven wheels or of the driven axle--which is obtained by differentiation of the output signal of the high-resolution sensor or sensors--and the vehicle longitudinal acceleration from the vehicle longitudinal acceleration sensor. The difference is used as control variable which is then processed further in a familiar manner, by comparing it with thresholds, to form control signals for wheel brakes and/or the vehicle driving engine.
After the predetermined speed threshold is exceeded, the system then switches over to the known signal production by the less sensitive sensors of the non-driven wheels to determine the vehicle speed.
In this manner, it is possible to obtain usable signals at justifiable costs from only about 0.3 to 0.5 km/h, instead of the previously usual 2.5 km/h, and thus to prevent excessive torques becoming apparent very early.
An application in a three-channel control system is particularly advantageous since only one single expensive sensor is required at the driving pinion of the driven axle and the former also exhibits a higher speed of rotation than the wheels, so that a usable sensor signal is available here even before one would be available at the wheels. After switching over to the normal speed sensor signal production, this "sensitive" sensor signal can be converted, by frequency conversion, for example by a frequency divider, to a frequency which is directly comparable to the signals of the "insensitive" sensors.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.